# Acoustic Emission Mechanisms and Fracture Mechanisms in Reinforced Concrete Beams Under Cyclic Loading and Unloading

## TL;DR

This study shows how acoustic emissions can detect and identify damage in reinforced concrete beams during cyclic loading, improving structural health monitoring.

## Contribution

A new damage model combining acoustic emission features achieves 88.89% accuracy in identifying damage stages.

## Key findings

- Acoustic emission signals correlate with mesoscopic fracture mechanisms in reinforced concrete beams.
- The Felicity Ratio enables earlier detection of irreversible damage compared to macro-mechanical indicators.
- An FR-Freq model using time and frequency-domain features identifies damage stages with high accuracy.

## Abstract

What are the main findings?
The correlation between mesoscopic fracture mechanisms and acoustic emission mechanisms in reinforced concrete beams under cyclic loading is revealed by integrating acoustic emission and digital image correlation techniques.Acoustic emission signals with distinct spectral characteristics are excited by mesoscopic fracture mechanisms corresponding to different damage stages.

The correlation between mesoscopic fracture mechanisms and acoustic emission mechanisms in reinforced concrete beams under cyclic loading is revealed by integrating acoustic emission and digital image correlation techniques.

Acoustic emission signals with distinct spectral characteristics are excited by mesoscopic fracture mechanisms corresponding to different damage stages.

What are the implications of the main findings?
Compared to macro-mechanical indicators such as fracture energy, the acoustic emission parameter Felicity Ratio enables earlier quantification of irreversible damage accumulation.An FR-Freq damage model incorporating both time-domain and frequency-domain acoustic emission features is proposed, achieving damage stage identification with an accuracy of 88.89%.

Compared to macro-mechanical indicators such as fracture energy, the acoustic emission parameter Felicity Ratio enables earlier quantification of irreversible damage accumulation.

An FR-Freq damage model incorporating both time-domain and frequency-domain acoustic emission features is proposed, achieving damage stage identification with an accuracy of 88.89%.

This study aims to elucidate the deterministic correlation between the microscopic fracture mechanisms and the multi-domain characteristics of acoustic emission in reinforced concrete beams under cyclic loading. Cyclic incremental tests were designed and conducted, with synchronized application of digital image correlation and AE techniques to capture the entire damage evolution process and corresponding signal responses throughout. The findings reveal that the damage stage division based on mechanical responses is consistent with that based on AE responses. Damage accumulation and irreversible processes can be clearly characterized by AE activity, and the systematic decrease in the Felicity ratio quantitatively verifies the irreversible accumulation of damage. Under cyclic loading, different microscopic fracture mechanisms generate AE frequency-domain signatures with statistically significant differences. A damage identification model integrating the Felicity ratio and multi-band energy features was developed, achieving an accuracy of 88.89% in identifying macroscopic damage stages. This research quantitatively confirms the effectiveness of AE characteristics as reliable identifiers of microscopic fracture mechanisms, providing a new basis for advancing structural health monitoring technologies grounded in fracture mechanism recognition.